The present invention is generally related to measurements of the eye, and in a particular embodiment, provides methods, systems, and devices for measuring a position of an eye during laser eye surgery.
Laser-based systems are now used in opthalmological surgery on corneal tissues to correct vision defects. These systems use lasers to achieve a desired change in corneal shape, with the laser removing thin layers of corneal tissue using a technique generally described as ablative photodecomposition. Laser eye surgery techniques are useful in procedures such as photorefractive keratectomy, photothcrapeutic keratectomy, laser in situ keratomileusis (LASIK), and the like.
The ability to track or follow movements of a patient's eye is recognized as a desirable feature in laser eye surgery systems. Movements of the eye include both voluntary movements and involuntary movements. In other words, even when the patient is holding "steady" fixation on a visual target, eye movement still occurs. Tracking of the eye during laser eye surgery has been proposed to avoid uncomfortable structures which attempt to achieve total immobilization of the eye. Tracking may enhance known laser eye surgery procedures, and may also facilitate new procedures, such as treatment of irregular astigmatism.
A variety of structures and techniques have been proposed for both tracking of eye movements and scanning of a laser beam across the corneal tissue. An exemplary linear array eye-tracking system and method are described in co-pending U.S. patent Ser. No. 09/365,428 filed on Aug. 2, 1999, the full disclosure of which is incorporated herein by reference. Other systems for tracking movement of an eye, particularly for use in laser eye surgery, arc described in U.S. Pat. Nos. 5,865,832; 5,632,742; and 4,848,340, the full disclosures of which are also incorporated herein by reference.
An exemplary "offset imaging" scanning system for selective ablation and sculpting of corneal tissue is described in European Patent Application Publication No. 628298, the full disclosure of which is hereby incorporated by reference. This offset imaging system allows a relatively laser beam to be accurately directed on to a surface of a corneal tissue so as to mitigate myopia, hyperopia, astigmatism, and combinations of these ocular defects, particularly when the scanning or offset imaging system is combined with one or more variable apertures for profiling the laser beam. As described in co-pending U.S. patent Ser. No. 09/274,499, filed on Mar. 23, 1999, entitled Multiple Beam Sculpting System and Method (the disclosure of which is incorporated herein by reference), the laser beam may ideally be separated into a plurality of beamlets to minimize discontinuities adjacent the ablation edges. Alternative scanning systems are described in the following U.S. Patents, which are also incorporated herein by reference: U.S. Pat. Nos. 5,556,395; 5,683,379; 5,391,165; and 5,637,109.
Although known scanning systems have proven both effective and safe for sculpting the cornea to improve vision, work in connection with the present invention has shown that integrating eye-tracking capabilities into known laser eye surgery systems can present significant challenges. For example, known laser eye surgery systems often include an optical imaging path which is co-axial with, and shares optical elements of the laser delivery system. While it has previously been proposed to utilize imaging-based tracking systems, this shared optical path can limit the available imaging contrast, and therefore the effectiveness of the tracking arrangement.
In light of the above, it would be desirable to provide improved laser eye surgery systems, devices, and methods. It would also be desirable to provide improved eye-tracking techniques, particularly for use with laser eye surgery, with the tracker ideally providing both lateral tracking and information regarding the position of the eye along the optical axis. It would be especially beneficial if these improvements provided enhanced tracking effectiveness and allowed the incorporation of eye-tracking capabilities into known laser eye surgery systems, ideally without having to modify the laser delivery system.